Jetting, also known as jet marks or jet salivation, refers to the products that occur 65 depending on the streamline in the gate, mostly in the mold for the side gate. When high-speed plastic melts through the nozzle, the runner and gate after narrow area, suddenly into the open and wide area, the molten material will be as bending forward along the flow direction, such as snakes, rapid cooling after contact with the mold surface. Because this part of the material cannot be well with the follow-up into the cavity of the resin, it caused obvious flow lines on the products. Under certain conditions, the resin is initially ejected from the nozzle at a relatively low temperature. Before touching the cavity surface, the viscosity of the resin becomes very large, thus producing a snake-shaped flow. As the higher temperature melt continues to enter the cavity, the initial material is pushed deeper into the mold, leaving the jet marks. Do you know how it was produced?
- Causes of mold and nozzle
Due to improper operation of process conditions, the local temperature at the nozzle and the melt temperature are too high or the residual pressure in the cylinder is too high. At this time should be appropriate to reduce the temperature of the nozzle or reduce the temperature of the cylinder or shorten the molding cycle and in the nozzle set filter material network. Appropriately reducing the injection pressure and reducing the residual pressure time, shortening the injection time, in addition, the nozzle hole is too large will also produce salivation. Small orifice nozzles should be used instead, or spring-needle valve nozzles and tilting nozzles should be used.
- The raw materials do not meet the requirements.
Molding material moisture content is too high will cause nozzle salivation. Raw materials should be pre-dried or a hopper dryer should be used.
- Cause of the low-pressure injection molding process
It may be due to the problems in the process of low-pressure injection molding that the temperature of the nozzle is too high, the raw material temperature is too high, the pressure of low-pressure injection molding is too high, the time of low-pressure injection molding is too long, and the injection cycle time is too long. In order to prevent the nozzle from salivating, a device to release the residual stress in the collector cavity should be installed in the hot runner mold.
The traditional mold design and process parameter setting mainly depend on the designer’s experience and skills, the rationality of mold design only depends on repeated trial and repair, the production cycle is long, the cost is high, the quality is difficult to guarantee. Simulating the forming process of this problem can be found in the design of before the mold manufacturing, mold design and process parameter Settings based on scientific analysis, can shorten the production cycle, improve the quality of products. With the improvement of product quality requirements, forecasting the forming process design has become an indispensable link. Therefore, it is of great significance to establish the mathematical model of melt flow and heat transfer in the mold cavity during injection molding and to use the numerical simulation method to simulate the molding process.